[PATCH] rs6000 improve handling of built-in initialization [PR95952]

[PATCH] rs6000 improve handling of built-in initialization [PR95952]

  Handle a scenario with a combination of old hardware, gcc-8 and
binutils where gcc will ICE during it's selftest.  This ICE was exposed
when the builtin processing for better #pragma support was added, where
we no longer skip builtin initialization based on the current mask.

Per the bug report and assorted debug, the ICE occurrs when building
the gcc-8 branch on a 970* based system with an old binutils.  (gcc-9 and
newer is OK.  binutils 2.34 is reported to allow success).

The attached patch adds a clause to the builtin initialization to skip
initialization of a builtin when the builtin mask is set but the icode
value is zero.   The subsequent assert check remains in place.

2020-07-13  Will Schmidt  <will_schmidt@vnet.ibm.com>

gcc/ChangeLog:

	PR target/95952

	* config/rs6000/rs6000.c (altivec_init_builtins): Add continue clause to
	predicate builtin handling.